Eric found a good way to pass the DoD with a Dissolve.Based on this I created two Macros:

Switch has an A and a B input. The Input-Control allows to switch between them. Other than the Dissolve-Tool this macro does preserve the Domain of Definition (DoD).

SwitchProxy is used to switch Full and Proxy resolution inputs based on the composition's Proxy-Setting. You can also force a manual output.

Pretty self-explanatory. Of course there is the excellent Switch Fuse by Tilt but for the simple Switch Macro you don't need anything to be installed first. If you want to Switch between more than two inputs the Fuse is for you.

Please Note:If falls back to the available input if only one was supplied (Dissolve behavior). But the DoD will mismatch based on the setting. I might fix this in future versions.